Process of oxidizing aldose sugars and products resulting therefrom



Patented Oct. 16, 1934 UNITED STATES PROCESS OF OXIDIZING ALDOSE SUGABS AND FROM Horace S. Isbell, W

PRODUCTS RESULTING THERE- n, n. 0.. mimic the Government i tl i lanited States,

mrented by the Secretary oi Commerce No Drawing.

Application February 21, 1031, Serial No. mm

Claims. (01. 204-9) (Granted under the'aot oi March 3, 1883, as amended April 30, 1928; 370 O. G. 757) The invention described herein may be manuiactured and used by or ior the Government ior governmental purposes without the payment to me oi any royalty thereon.

5 The present invention relates to a process of preparing monocarboxylic acids and their salts.

It is an object oi the present invention to provide an improved process ior the oxidation oi aldose sugars to their acids and salts. Other objects oi the invention will appear more iully from the iollowing specification.

Heretoiore, various methods have been used ior the oxidation oi aldose sugars, but these have not been wholly satisiactory. For example, ii oxidation is effected by bromine or chlorine a large quantity is necessary, and two molecules oi hydrogen bromide or hydrogen chloride are iormed ior each molecule oi sugar which is converted to acid. This large amount of hydrogen 2 bromide or hydrogen chloride seriously interieres with the separation of the desired product. 0r.

ii electrolytic oxidation is-resorted to, a smooth oxidation to the corresponding monocarboxylic acid is not obtained, many degradation products being produced which are difllcult to separate and which have little or no practical value.

In accordance with the present invention, these undesirable results are overcome by a process wherein oxidation is eflected electrolytically in the presence oi a catalyst. As a result, a nearly quantitative oxidation of the sugar into its monocarboxylic acid is obtained, without objectionable by-products. The catalyst, in addition to expediting the desired reaction, causes an increase in the conductivity oi the solution, thus reducing its resistance and hence the amount oi energy required to eflect the desired oxidation.

At the same time, the invention contemplates, among other things, the use oi a base or buffer in the process, in the event that a salt of the sugar 40 acid is desired. The buffer has the additional advantage that a nearly neutral solution may be used in the process; and the current eniciency (that is, actual oxidation divided by theoretical oxidation) is remarkably increased.

In the practice oi the invention, satisiactory results have been obtained with such catalysts as bromine, hydrogen bromide, or halogen salts of higher atomic weight than chlorine, such as sodium bromide, calcium bromide, and iodides in slightly alkaline solution. As a bufler or base,

satisiactory results have been obtained with lime,

calcium carbonate, barium carbonate and magnesium oxide.

It the process oi the present invention is used.

in connection with such aldose sugars as glucose,

then the several steps are conveniently as iollows: approximately 45 grams oi glucose, 10 grams oi-a catalyst, say, sodium bromide, and one liter oi water are placed in an electrolytic cell which may take the iorm of a container provided with a platinum cathode and a graphite anode. It is noted that these proportions may be varied within wide limits without departing irom the spirit and scope oi the invention. About 14 ampere-hours oi electricity are now passed through the solution and, at the same time, the solution is preierably agitated by means oi a conventional mechanical stirrer. When the sugar determinations, by some such method as iodine titration, show that the oxidation oi the aldose sugar to gluconic acid is substantially complete, electrolytic action is terminated. Thus, the sugar has been nearly quantitatively converted into gluconic acid. The reaction is represented by the iollowing equation:

This gluconic acid may be used as such or it may be separated as calcium gluconate in the usual manner. Should it be desirable to form the calcium gluconate direct, then the iollowing process may be used, it being noted that the proportions are approximate only and given by way oi illustration: approximately 90 grams oi glucose, 10 grams oi calcium bromide, 25 grams of a bufier, such as calcium carbonate, and one liter of water, are placed in an electrolytic cell provided, say, with graphite electrodes and the conventional mechanical stirrer. A direct current of about 0.5 amperis is now passed through the solution and the progress of the reaction iollowed by sugar determinations. After 27 amperehours oi current has been used, the reaction is practically complete, only a small amount oi unconverted sugar remaining in the solution. Upon cooling the solution and nucleation, a good yield oi crystalline calcium gluconate is obtained which is separated in the usual manner. The mother liquors, which contain the catalyst, may be used ior a second oxidation by merely adding additional glucose and calcium carbonate and repeating the process. The ioregoing reaction is represented by the following equation:

being approximate only: ten grams of calcium bromide, 40 grams of mlose, 15 grams of a buller, such as calcium carbonate,- and one liter of water are placed in an electrolytic cell of the usual type and a current of about 0.3 amperes passed through the solution. After 15 amperehours of current, a Fehling's test for sugar is negative, indicating that substantially all the xylose had been converted into .xylonic acid, which in turn has reacted with the calcium carbonate to give calcium xylonate. The action may be represented by the following equation:

In accordance with the present invention, the calcium xylonate may be separated from the solution in the following manner: the solution preferably is concentrated to a convenient volume, say, 200 ml., and an excess of lime, say 25 grams, is added. After standing a short time, an insoluble basic salt precipitates which may be separated in the usual manner. This salt is a new substance which affords a convenient method for the separation of calcium xylonate. The normal calcium xylonate may be obtained from this new basic salt by removing the lime with carbon dioxide, the reaction being represented by the following equation:

Should the free acid be desired, it may be formed in accordance with the present invention by removing the calcium with an acid, say, sulphuric or oxalic acid, in the usual manner. Or, the free acid may be obtained directly from xylose by electrolytic oxidation in the presence of a catalyst such as bromine or a bromide.

As a further illustration of the invention, the application of the process to the aldose sugar galactose is as follows, the proportions being approximate only and given by way of illustration: about 50 grams of galactose are dissolved in one liter of water containing seven grams of hydrogen bromide. The solution is conveniently placed in the anode compartment of a diaphragm type of cell containing a mechanical stirrer. A direct current of about 0.4 amperes is then passed between the electrodes. After about 15 amperehours of current has been used, the reaction is practically complete. The hydrogen bromide preferably is removed at the end of the reaction by continuing the electrolysis which converts the hydrogen bromide into free bromine and hydrogen. Removal of the bromine is expedited by blowing a stream of air through the solution, the resulting bromine vapors being conveniently recovered by absorption in an alkali. A nearly pure solution of galactonic acid is obtained by this means from which crystalline galactonic lactone may be obtained by evaporation to a thick syrup.

While the invention has been discussed in detail in connection with certain aldose sugars, it

' is also applicable to other sugars of this group such as lactose, manncee, and arabinose. It is also noted that the foregoing proportions are susceptible of change within relatively wide limits and are set forth by way of illustration only. The invention may be further modified and embodied within the scope of the subioined claims.

I claim:

l. The process which comprises the electrolytic oxidation of an aldose sugar in the presence of a halogen salt of higher atomic weight than chlorine.

2. The process which comprises the electrolytic oxidation of an aldose sugar in the presence of bromine.

3.Theprocess of oxidizinganaldosesugar which comprises passing an electrical current through a solution containing an aldose sugar,

a bromide and a calcium compound adapted to combine with an organic acid to form a salt.

4. The process which comprises the electrolytic oxidation of xvlose in the presence of a bromide and a calcium compound adapted to combine with xylonic acid to form calcium xylonate.

5. As a new product, a basic calcium xylonate having the formula Ca(CsI-Is0s) 2.2CaO, H20.

6. The process which comprises the electrolytic oxidation of xylose in the presence of a bromide and a calcium compound adapted to combine with xylonic acid to form calcium xylonate, and then adding at least two molecular equivalents of lime for each equivalent of calcium xylonate so as to cause the separation of a basic calcium xylonate. I

'l. The process of forming xylcnic acid which comprises removing the calcium from iio Ca (CsHaOe) 2.2C8-O,

E20 by means of an acid which forms a difllcultly soluble calcium salt. V

8. The process of forming xylonic acid which comprises the electrolytic oxidation of xylose in the presence of a bromide. 4

9. The process which comprises the electrolytic oxidation of an aldose sugar in the presence of a bromide, and then reclaiming bromine from the. bromide by further electrolysis.

10. Process for converting an aldose into the corresponding aldonic acid, comprising electrolyzing an aqueous solution of the aldose in the presence of a bromide.

11. Process for converting an aldose into the corresponding aldonic acid, comprising electrolyzing an aqueous solution of the aldose on a carbon anode in the presence of a halogen salt of higher atomic weight than chlorine.

12. An electrolyte for the electrolytic conversion of an aldose into the corresponding aldonic acid, comprising an aqueous solution of the aldose containing a bromide compound in the proportion of less than 1 equivalent of the aldose pres- 1 ent.

13. A process for converting an aldose into the corresponding aldonic acid, comprising electrolyzing through a diaphragm an aqueous solution of the aldose in the presence of a bromide.

14. A process for converting an aldose into the corresponding aldonic acid, comprising electrolyzing an aqueous solution of the aldose in the presence of a bromide, the reaction of the solution being on the acid side of neutrality.

15. The process of oxidizing an aldose sugar which comprises passing an electrical current through a solution containing an aldose sugar, a bromide and calcium carbonate.

16. The process which comprises the electrolytic oxidation of glucose in the presence or a bromide and a calcium compoimd capable of combining with gluconic acid to form calcium gluconate, the reaction occurring on the acid side or neutrality.

17. The process which comprises the electrolytic oxidation 01 glucose in the presence of a bromide and calcium carbonate.

18. An electrolyte for the electrolytic oxidation of an aldose, comprising a solution of the aldose containing a bromide compound in the propor- 

